Describe an activity to show that a current-carrying conductor experiences a force in a magnetic field. State the rule that gives the direction of the force.

1. 1 · Open with the idea. A current-carrying conductor placed in a magnetic field experiences a force.
2. 2 · Describe the set-up.
   • Hang an aluminium rod horizontally from a stand.
   • Place it between the poles of a horseshoe magnet, with the field upwards.
   • Connect a battery, a key and a rheostat in series with the rod.
3. 3 · Draw it. [Horseshoe magnet with the rod between its poles; arrows for the current, the field and the direction the rod moves]
4. 4 · Write the observations.
   • The rod moves when the key is closed.
   • Reversing the current reverses the motion.
   • Reversing the field reverses the motion.
   • The force is largest at right angles.
5. 5 · State Fleming's left-hand rule. Thumb, forefinger and middle finger of the left hand at right angles: forefinger along the field, middle finger along the current, thumb gives the force.
6. 6 · Real life. Phone speakers move because of this force, and MRI scans use magnetism to see inside the body.
7. 7 · Close in one line. The force depends on the directions of both the current and the field.

Scoring tip: Say 'left hand' clearly. Mixing it up with the right-hand thumb rule costs marks.